As the label for control of articles such as labels attached to plastic containers used for transporting foods (good-delivery boxes), labels used for control of electronic parts and labels attached to cardboard boxes for control of distribution of articles, currently, labels having a heat-sensitive recording material (direct thermal papers and the like) as the surface stock are mainly used.
In the heat sensitive recording material, a heat sensitive recording layer containing an electron-donating and, in general, colorless or lightly colored dye precursor and an electron-accepting color developing agent as the main components is formed on a support. By heating the heat sensitive recording material by a heated head or a heated pen, the dye precursor and the color developing agent react instantaneously with each other, and a recording image can be obtained. Once the image is formed, it is impossible that the image in the heat sensitive recording material described above is erased to restore the condition before being treated for the image formation.
Heretofore, a heat sensitive recording material described above is used as the surface stock in the labels used for the control of distribution of articles described above, and information such as the address, the name of the sender, the name of the article, the number and the weight of the article, the date of production, the best-before date, the specific identification number and the lot number or the bar code expressing the information is printed using a thermal printer of the contact type, and the obtained label is attached to the adherend. When the object assigned to the label is achieved, the label is manually removed so that the adherend such as a container and a card board box can be utilized again, and great amounts of time and labor are required for the removal. Another label is attached to the adherend from which the previous label has been removed, and the adherend is used again.
As described above, it is the actual situation at present that a label is removed and another label is attached every time the adherent is used repeatedly. Therefore, a rewritable thermal label which can be used repeatedly for recording and erasing information while the label is not removed from the adherend in each reuse of the adherend but remains attached to the adherend is attracting attention. For example, a reversible heat sensitive recording material of the non-contact type having a means for recording and erasing visible information which is obtained by forming a heat sensitive color developing layer containing a dye precursor and a reversible color developing agent on a support is developed (for example, refer to Patent References 1 to 3). A combination of a rewritable recording medium allowing rewriting visible information and an IC tag allowing rewriting invisible information is also disclosed (refer to Patent Reference 4).
When the recording of visible information is repeated a plurality of times by rewriting and/or erasing with laser light in the non-contact manner, a problem arises in that the surface of the recording medium is destroyed with heat due to the laser light applied repeatedly. Although the destruction can be suppressed by using a material for laser light absorption and heat conversion, the problem cannot be overcome completely. Other problems arise in that dirt is attached to the recording medium to cause trouble in printing and that other articles and containers hit the surface of the recording medium to deform or detach the recording medium and impair the function of the IC tag.
[Patent Reference 1] Japanese Patent Application Laid-Open No. 2003-118238
[Patent Reference 2] Japanese Patent Application Laid-Open No. 2006-231647
[Patent Reference 3] Japanese Patent No. 2741435
[Patent Reference 4] Japanese Patent Application Laid-Open No. 2004-265249